The use of NMR for determination of new structures in irradiated TFE/PMVE fluoropolymers

The radiation chemistry of two TFE/PMVE copolymers with TFE mole fractions of 0.66 and 0.81 has been studied under vacuum using ⁶⁰Co γ-radiation over absorbed dose ranges up to 4.2 MGy. The radiolysis temperature was 313 K for both TFE/PMVE copolymers. New structure formation in the copolymers was identified by solid-state ¹⁹F NMR and the G-values for new chain ends of 2.1 and 0.5 and for branching sites of 0.9 and 0.2 have been obtained for the TFE/PMVE with TFE mole fractions of 0.66 and 0.81, respectively. The relative yields of –O–CF₃ and –CF₂–CF₃ chain ends were found to be proportional to the copolymer composition, but the yields of the –CF₂–CF₃ chain ends and –CF– branch points were not linearly related to the composition, rather they were correlated with the radical yields measured at 77 K.     

The role of air in the radiolytic degradation of polycarbonate

Bisphenol A polycarbonate (PC) was irradiated with Co-60 γ-rays at room temperature in presence of air or nitrogen. Changes were followed by IR and NMR spectroscopy as well as GPC, X-ray diffraction, melting temperature, DTA, and isothermal TG. The changes observed include chain scission, chain branching/cross-links, decrease in thermal stability, crystallinity and scission of the product. However, there are some differences in samples irradiated in presence of air as opposed to those irradiated in nitrogen, but many changes are similar. Air accelerates the radiolytic degradation of PC. The radiochemical yield of chain scission, G(s), increased to 0.20 from 0.13; the chain branching/cross-links are less numerous as compared to those after irradiation in nitrogen the thermal stability decreases along with the temperature of that rate of maximum mass loss, crystallinity and the melting temperature. The chemical products in both air and nitrogen irradiations are almost identical. The formation of these products could be explained by multiple pathways-free radical formation and by ring as well as side chain attack. The studies suggest that Fries' rearrangement is not an important pathway during the radiolytic degradation as compared with photodegradation.     

Photodegradation of cellulose acetate fibers

The photodegradation of cellulose acetate fibers by ultraviolet light in vacuo at 77°K and at ambient temperature was studied. Three kinds of light sources with different wavelengths between 2353 and 6000 Å were employed. ESR studies at 77°K show that several kinds of free radicals are produced from cellulose diacetate (CDA) and cellulose triacetate (CTA) fibers when irradiated with light of wavelength shorter than 2800 Å. Among these methyl radicals formed decayed within 210 min at 77°K. When the temperature was raised above 77°K, radical transformation occurred at 87°K and most of the free radicals decayed at 193°K, whereas the cellulosic radicals were stable at this and even at higher temperatures. Ultraviolet spectroscopy studies revealed that the main chromophores are the carbonyl function of the acetyl group and acetal groups in the polymer. The photodegradation of the polymers at ambient temperature resulted in the formation of gaseous products (mainly CO, CO₂, and CH₄), together with the loss of bound acetic acid content and sample weight. Decreases in viscosity and reduction of tensile strength and elongation were also observed in the irradiated samples, revealing that the overt effects of ultraviolet light on cellulose acetate fibers are interpreted in terms of free-radical reactions ultimately leading to main-chain and side-group scissions, unsaturation, and the formation of small molecule fragments. Among these, main-chain scission took place predominantly in CDA fiber and side-group scission in CTA fiber. The mechanism of the fundamental photochemical degradation processes of cellulose acetate fibers is elucidated.     

An ESR and NMR study of the gamma radiolysis of a bisphenol-A based polycarbonate and a phthalic acid ester

A study of the γ-radiolysis of the commercial polymers U-polymer, UP (Unitake) and polycarbonate, PC, (Aldrich) has been undertaken using ESR spectroscopy. The G-value of radical formation at 77 K has been found to be 0.31±0.01 for UP and 0.5±0.02 for PC. By using thermal annealing and spectral subtraction, the paramagnetic species formed on irradiation has been assigned. The effect of radiation on the chemical structure of UP and PC has been investigated at ambient temperature and at 423 K. The NMR results show that a new phenol type chain end is formed in the polymers on exposure to γ-radiation. The G-value of formation of the new phenol ends was estimated to be 0.7 for PC (423 K) and 0.4 for UP (300 K). © 1998 John Wiley & Sons, Ltd.     

Effect of G/M ratio on the radiation-induced degradation of sodium alginate

Radiation-induced degradation of sodium alginate (NaAlg) having different G/M ratios was investigated. NaAlg samples were irradiated with gamma rays in air at ambient temperature in the solid state at low dose rate. Change in their molecular weights was followed by size exclusion chromatography (SEC). Changes in their rheological properties and viscosity values as a function of temperature, shear rate and irradiation dose were also determined. Chain scission yields, G(S), and degradation rates were calculated. It was observed that G/M ratio was an important factor controlling the G(S) and degradation rate of sodium alginate.     

二氯二茂钛引发二苯乙炔聚合的研究

在高温下 ,二氯二茂钛受光照引发二苯乙炔聚合 ,得到结晶度为 95 %的聚二苯乙炔 .经红外、质谱、热分析、X光衍射、元素分析等方法 ,确定其结构为顺顺式螺旋刚性棒状结构 ,形成假六方晶系堆积 ,螺旋柱直径即螺旋轴间距为 1 46nm ,其特征红外吸收峰位于 1179cm-1和 115 6cm-1.在聚合引发阶段中止反应 ,分离出聚合中间体六苯基苯 .根据不同温度时聚合转化率与时间的关系曲线 ,测得聚合活化能为 2 6× 10 5J/mol.热分析表明 ,结晶聚二苯乙炔在 493K至 5 73K比较稳定 ;在 713K的吸热峰显示出破坏晶格的能量 .根据聚合反应诱导期长、中间体和聚合物的结构以及阻聚反应 ,推断聚合过程中二氯二茂钛受光照产生二氯化钛 ,催化二苯乙炔进行均相定向聚合 .结晶聚二苯乙炔电导率小于 10 -12 (Ωcm) -1.     

Efficiency of radiation-induced main-chain scission of poly (methyl methacrylate) depends on the irradiation temperature because of coexisting monomer

Effect of irradiation temperature on the main-chain scission of poly (methyl methacrylate) (PMMA) caused by γ-irradiation was studied by means of gel permeation chromatography and ESR spectroscopy. Although no temperature dependency was observed on the scission efficiency for purified PMMA, the efficiency for crude or monomer-doped purified PMMA was decreased by decreasing the temperature below ca. 200 K. Above 200 K the efficiency was constant and did not depend on the purity of PMMA. ESR study of the irradiated PMMA revealed that the suppression of the scission below 200 K is induced by the addition of methyl methacrylate monomer to primary radical species, which otherwise cause the main-chain scission by warming the polymer above 200 K. The primary radical generated above 200 K immediately converts to the scission-type ? CH₂ ? ?(CH₃) COOCH₃ radical through the β-scission of the polymer main chain, so that the efficiency of the scission does not depend on both the impurity and the irradiation temperature. © 1994 John Wiley & Sons, Inc.     

The thermo-oxidative degradation of polyolefines—Part 10. Correlation between the formation of carboxyl groups and scission in the oxidation of polyethylene in the melt phase

Films of low density polyethylene have been degraded under an oxygen atmosphere at temperatures above the semicrystalline melting point. Time, conversion and temperature dependence of carboxyl group formation and chain scission have been studied. After induction periods we found linear dependences both in function of time and conversion. One third of absorbed oxygen forms carboxyl groups and the absorption of 3·57 mmol oxygen per monomer unit is needed for one chain scission. Maximum rates of carboxyl formation and chain scission have Arrhenius temperature dependence with 33·5 kcal/mole activation energy. The number of carboxyl groups and chain scissions are always practically the same; we assume that the isomerisation of secondary alkyl peroxy radicals simultaneously causes chain scission and carboxyl formation.     

γ-Irradiation of Nylon 6

Viscosity, Infra-red, NMR spectral measurement technique, density measurement, and electrical conductivity were used to study the changes that occured during γ-radiolysis of Nylon 6. It was observed that it undergoes chain scission and crosslinking, but chain scission predominates over crosslinking in air irradiation. From melting temperature, density measurement, and the use of the Flory equation the enthalpy of fusion of Nylon 6 is 11.86 and 13.84 kJ/mol in an inert atmosphere and in air irradiation, respectively. The indirect effective band gap decreases and electrical conductivity increases when Nylon 6 is irradiated with γ-rays.     

Synthesis of persulfate containing poly (N-vinyl-2-pyrrolidone) (PVP) hydrogels in aqueous solutions by γ-induced radiation

The effect of ⁶⁰Co γ-irradiation on aqueous solutions of poly(N-vinyl-2-pyrrolidone) (PVP) in the presence of persulfate anion has been investigated. The gelation dose of PVP and persulfate containing PVP aqueous solutions has been determined. At low concentrations of persulfate (1.00–3.50%), gelation percentages exhibited a decreasing trend by increasing persulfate content in aqueous solutions of the polymer. The gelation doses of persulfate containing polymer solutions were calculated by the Charlesby–Pinner equation. It was observed that the gelation dose values were shifted to higher values by increasing persulfate concentration in solution. The ratio of the chain scission and crosslinking yields (G(s)/G(x)) was also determined. The results showed that the G(s)/G(x) ratios were smaller than one for PVP aqueous solution system, whereas those obtained for persulfate containing PVP aqueous solutions were higher than unity. The results implied that the chain scission of polymer is more effective than crosslinking in the presence of persulfate. Mechanism of the crosslinking and/or degradation and structure–property relationship of PVP and PVP/persulfate hydrogel systems were investigated by Fourier transformation infeared and thermal analysis (differential scanning calorimetry, thermal gravimetric analysis and differential thermai analysis) methods.     

Radiation effect studies on anticancer drugs, cyclophosphamide and doxorubicin for radiation sterilization

Two anticancer drugs, cyclophosphamide (CPH) and doxorubicin hydrochloride (DOXO), in powder form were exposed to a range of doses of ⁶⁰Co gamma and electron beam radiation to study the effects of ionizing radiation. Pharmacopoeia tests, discolouration, degradation products, effect of irradiation temperature and dose rate were investigated. CPH undergoes less than 2% degradation at 30 kGy. Chromatographic studies revealed formation of several trace level degradation products, discolouration and free radicals in the irradiated CPH. N,N-bis (2-chloroethyl) group in the molecule is particularly sensitive to radiation degradation. Irradiation to 5 kGy at low temperature (77 K) did not result in significant changes. DOXO was observed to be quite radiation resistant and did not undergo significant changes in its physico-chemical properties and degradation product profile. It can be radiation sterilized at normal sterilization dose of 25 kGy.     

Effect of temperature in region of γ and β relaxations on photo-oxidation of polystyrene

Atactic polystyrene films were irradiated at 254 nm in oxygen. The influence of the polystyrene mobility on chain scission and acetophenone formation in the temperature range 233–387 K has been studied. The increase of quantum yield for chain scission in the γ relaxation region was attributed to phenyl group rotation and increase of the probability of energy transfer from this chromophore to induce C-H bond scission. The considerable increase of acetophenone formation at the β relaxation was attributed to increase of oxygen interaction with the chromophore because of cooperative motion of main chain and benzene rings.     

Melting and thermal decomposition of [Ni(H2O)6](NO3)2

The two-stage melting process and the thermal decomposition of [Ni(H₂O)₆](NO₃)₂ was studied by DSC, DTA and TG. The first melting point at 328 K is connected with the small and the second melting point at 362 K with the large enthalpy and entropy changes. The thermal dehydration process starts just above ca. 315 K and continues up to ca. 500 K. It consists of three well-separated stages, but the sample mass loss at each stage depends on the experimental regime. However, irrespective of the chosen regime, the total of registered mass losses in stage one and two amounts to three H₂O molecules per one [Ni(H₂O)₆](NO₃)₂ molecule. The remaining three H₂O molecules are gradually freed in the temperature range of 440–500 K in the third stage of the dehydration. Above 580 K, anhydrous Ni(NO₃)₂ decomposes into NO and NiO. The gaseous products were identified by quadrupole mass spectrometer (QMS), and the solid product was identified by X-ray diffraction (XRD) analysis.     

Radiation crosslinking and scission of poly(vinyl methyl ether) in aqueous solution

For a wide range of poly(vinyl methyl ether) (PMVE) concentrations (1–16 g dm⁻³), in anoxic conditions, polymer-derived radicals recombine in two major pathways: (i) crosslinking and (ii) disproportionation. Both these processes proceed inter- and intramolecularly. The radiation-chemical yields and kinetics of crosslinking have been studied by pulse radiolysis with light scattering intensity detection (LSI). In the absence of oxygen, G-values of intermolecular crosslinking were determined on the basis of LSI changes versus applied dose and compared with the results obtained previously for γ-irradiated samples. It has been found that the first half-life time of intermolecular crosslinking decreases with increasing dose per pulse. Addition of small amounts of macroradical scavenger (cysteamine hydrochloride) decreases, drastically, the increase of LSI signal. On increasing the PVME concentration, intermolecular crosslinking becomes more efficient.

In the presence of oxygen, for diluted PVME solution (0.1 g dm⁻³), decrease of LSI signal consisting of the kinetic of a first-order reaction was observed. The rate constant of LSI decrease was found to be 1.1×10³ s⁻¹ and it was attributed to the main-chain scission.     

Radiolyse des hydrocarbures. 21e communication. Mécanismes radicalaires et non-radicalaires dans les n-alcanes en phase liquide

Contributions of radical and non-radical processes have been determined in the formation of radiolysis products of n-heptane, n-octane, n-nonane and n-decane in a large range of temperature. Calculations are based on the combination and the dismutation of radicals, both reactions having nearly the same importance. Hydrogen abstraction reactions become important above – 25°. Intermediate molecular weight products and dimers are formed by statistical combination of the various radicals resulting from C? C and C? H scission. At low temperature, low molecular weight products are formed by both radical and non-radical processes, the second one being more important (3/4 for alcanes and 2/3 for olefins). The yield of radicals increases with the chain length of the irradiated n-alkane and amounts to 4.5 for n-heptane and 6.8 for n-decane at – 25°. This increase is due only to radicals from C? H scission, while the yield of radicals from C? C scission remains constant. Scission of CH₂? CH₂ bonds is favored for bonds inside the molecule, but this affect diminishes with chain length and CH₂? CH₂ rupture is equally probable at all positions for n-alcanes heavier than decane. Methyl C? H scission is 2.7 times less probable than methylene C? H scission. The radiolysis of mixtures of protonated and deuterated n-alcanes is shown to be able to give information concerning basic processes in radiation chemistry.     

Vibrational spectra, conformations, ab initio calculations and vibrational assignments of 3-pentyn-2-ol

The infrared spectra of 3-pentyn-2-ol, CH₃CCCH(OH)CH₃, have been recorded as a vapour and liquid at ambient temperature, as a solid at 78 K in the 4000–50 cm⁻¹ range and isolated in an argon matrix at ca. 5 K. Infrared spectra of the solid phase at 78 K were obtained before and after annealing to temperatures of 120 and 130 K. The IR spectra of the solid were quite similar to that of the liquid.

Raman spectra of the liquid were recorded at room temperature and at various temperatures between 295 and 153 K. Spectra of an amorphous and annealed solid were recorded at 78 K. In the variable temperature Raman spectra, some bands changed in relative intensity and were interpreted in terms of conformational equilibria between the three possible conformers. Complete assignments were made for all the bands of the most stable conformer in which OH is oriented anti to C₁(a_Me). From various bands assigned to a second conformer in which OH is oriented anti to H_gem(a_H), the conformational enthalpy differences was found to be between 0.4 and 0.8 kJ mol⁻¹. The highest energy conformer with OH anti to C₃(a_C) was not detected.

Quantum-chemical calculations have been carried out at the MP2 and B3LYP levels with a variety of basis sets. Except for small basis set calculations for which the a_H conformer had slightly lower energy, all the calculations revealed that a_Me was the low energy conformer. The B3LYP/cc-pVTZ calculations suggested the a_Me conformer as more stable by 0.8 and 8.3 kJ mol⁻¹ relative to a_H an a_C, respectively. Vibrational wavenumbers and infrared and Raman band intensities for two of the three conformers are reported from B3LYP/cc-pVTZ calculations.     

Polycondensation of bis(p-nitrophenyl) β-truxinate with diamine

Model reaction of bis(4-nitrophenyl) β-truxinate (BNPT) with aliphatic amines proceeded quantitatively at room temperature. Accordingly, polycondensation of BNPT with various diamines was carried out at room temperature or 80°C. During the polycondensation of BNPT with diamines, the precipitation of polymer or the observed gelation of polymerization solution occurred, which may limit the molecular weight of the polymer. On the other hand, the reaction of BNPT with 1,3-(4-piperidyl)propane (DPP) proceeded homogeneously to give the polymer with relatively high molecular weight, and the obtained polyamide (P-1e) showed excellent solubility in many solvents. The study of TG and DTA indicated that the obtained polymers were stable at lower temperature than around 270°C. The polymer prepared from the polycondensation of BNPT with hexamethylenediamine showed melting point and decomposition due to the imidation at 282°C. The photochemical reaction of these polymers was carried out in the film state. The irradiation of 254 nm light caused an absorption at 272 nm to appear and the molecular weight to decrease. This meant that the scission of cyclobutane ring in the main chain occurred to give cinnamamide structures. Also, the absorption at 272 nm decreased by the irradiation of 302.5 nm light. However, the UV spectrum of irradiated polymer did not agree with that of the original polymer. These results suggested that the dimerization of the resulting cinnamamide moieties occurred in the competition of their trans–cis-isomerization. On the other hand, the rate of scission of cyclobutane ring of P-1e was faster than that of the corresponding polyamide containing α-truxillamide structure.     

Kinetics of oxidation of polycarbosilane films by oxygen

Using IR spectroscopy we have investigated the kinetics of oxidation of the Si-H bonds of polycarbosilane in the temperature range 423–493 K. We determined the effect of the oxidation temperature and oxidation time on the rate of the process and the thickness of the oxidized layer. We determined the activation energy.Institute of Surface Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 5, pp. 630–633, September-October, 1991. Original article submitted October 30, 1990.     

Irradiation effects on thermal,surface, and physicomechanical properties of ethylene and vinyl acetate copolymer

The structural and thermal transitions for ethylene and vinyl acetate copolymer (EVA) samples irradiated by fast electrons at doses in the range of 2.5–25 Mrad were investigated by DSC and X-ray diffraction analysis. The parameters of chemical bonds in the amorphous phase of copolymer were determined. The change in the degree of crystallinity, melting temperature, and crystallite sizes before and after radiochemical modification were estimated. The obtained results were analyzed and corresponded to the physicomechanical properties of copolymers. The surface energy of copolymers before and after irradiation was defined. The strength of adhesive joints based on EVA from PET substrates and the influence of radiochemical modification of adhesive before joint formation on its strength were analyzed.     

Effect of gamma Irradiation on Latex Film Dissolution

Latex films have been prepared by annealing pyrene (Py)-labeled poly(methyl methacrylate)-polyisobutylene particles at the glass transition temperature (100 degrees C). These films were then irradiated by gamma rays from (60)Co in a gamma cell at room temperature at various dose rates (rad/h). Before dissolution the films were annealed at 200 degrees C for a 30 min time interval to complete the film formation process. Steady-state fluorescence techniques were used to monitor the dissolution of irradiated latex films. Dissolution of films in a chloroform-heptane (80%-20%) mixture was monitored in real time by the Py fluorescence intensity change. Relaxation constants, k(0), and dissolution coefficients, D(d), of polymer chains were measured. Two different regimes of D(d) values were observed during dissolution, which are related to two different molecular weight distributions caused by scission and branching of polymer chains when they were irradiated and annealed. Copyright 2001 Academic Press.